Hello shabird,

Your regex says: match one or more word characters, followed by one or more non-word characters, followed immediately by a newline; and return the characters matched minus the newline. This won’t work.

What you need is a way to uniquely identify the IDs. From the file contents shown, it looks as though each ID is immediately preceded by a > character. If so, you could use something like this:

#! perl

use strict;
use warnings;
use Data::Dump;

my   @matches;
push @matches, mysub($_) for <DATA>;
dd  \@matches;

sub mysub
{
    return shift =~ / > (\S+) \s /gx;
}

__DATA__
 
>NM_030643.4 Homo sapiens apolipoprotein L4 (APOL4) 
GAGGTGCTGGGGAGCAGCGTGTTTGCTGTGCTTGATTGTGAGCTGCTGGGAAGTTGTGACTTTCATTTTA
CCTTTCGAATTCCTGGGTATATCTTGGGGGCTGGAGGACGTGTCTGGTTATTATATAGGTGCACAGCTGG
>NM_001198855.1 Homo sapiens cytochrome P450 family 2 subfamily C memb
+er 8 (CYP2C8)
ACATGTCAAAGAGACACACAC
>NR_029834.1 Homo sapiens microRNA 200a (MIR200A), microRNA
CCGGGCCCCTGTGAGCATC
>AC067940.1 Homo sapiens clone RP11-818E9, LOW-PASS SEQUENCE SAMPLING
AAATACAACTTTAAATCAAAACGGTAAAAATTCCACTCTTTCATACTAACTTCAAAAGTATTTGCTTTAA
AAAAAAAGNNNNNNNNN
[download]

Output:

23:46 >perl 2038_SoPW.pl
["NM_030643.4", "NM_001198855.1", "NR_029834.1", "AC067940.1"]

23:46 >
[download]

Hope that helps,